Field of the Invention
The invention relates to an S0-Interface for an ISDN base connection, through which a four-wire line with a receiver line pair and a transmitter line pair is connected, with potential separation, to an ISDN terminal device.
The double line coming in from an ISDN network is usually converted to a four-wire interface at a network socket of a user. That interface between the ISDN network and the terminal device is referred to as an S0-interface. The four-wire line is divided into a receiver line pair for incoming signals and a transmitter line pair for outgoing signals. The transmission-technological functions of the four-wire duplex process are implemented with a so-called S0-component, whereby the connection between the lines and the S0-component are obtained, via potential separation, with a respective transformer in the receiver line pair and in the transmitter line pair.
That potential separation has the disadvantage of increased damping due to parasitic ohmic loading by the transformer. Furthermore, the transformers that are required are relatively expensive.
The use of transformers may lead to problems in remote feeds. Insufficiently current-compensated transformers may reach saturation due to the direct current of the remote feed, which reduces the reach of the S0-interface.
It is accordingly an object of the invention to provide an S0-interface for an ISDN basic access connection, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which can be produced more inexpensively, yet satisfies the high demands for transmission quality.
With the foregoing and other objects in view there is provided, in accordance with the invention, an S0-interface for an ISDN base connection, comprising:
a four wire line with a pair of receiver lines and a pair of transmitter lines, the four wire line having an interface side and a device side;
a capacitor connected in each of the receiver line for potential separation between the interface side and the device side;
a transformer connected in the pair of transmitter lines for potential separation between the interface side and the device side; and
an inductance connected in each of the receiver lines and the transmitter lines on the interface side thereof.
In accordance with an added feature of the invention, each of the inductances is a winding with a respective core. In accordance with an alternative feature, the inductances have a common core.
In accordance with a concomitant feature of the invention, a voltage amplifier is connected to the pair of receiver lines at the device side thereof. The voltage amplifier having a voltage amplification equal to a voltage amplification of the transformer in the pair of transmitter lines.
The invention provides for the advantage that, in spite of principally different transmission characteristics between a transformer and a capacitor, the receiver line pair as well allows reaching an equally good transmission quality. Furthermore, there is provided protection for the S0-interface against lightning spikes. By connecting the line ends to a voltage amplifier it is prevented that incoming information may not be detected if the input level falls below a certain signal threshold. The voltage level detection may be dependably achieved by that compensation.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an S0-interface for an ISDN terminal, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of a specific embodiment when read in connection with the accompanying drawing.